Hello,
I have been programming in Python for many years and I've used it for many types of projects.
For this project I would build a Python application that regularly checks the GPIO port connected to the PIR sensor and starts record video from the USB webcam (probably using standard tools like ffmpeg or mencoder).
Sending the email would also be done by the Python application (using the builtin libraries).
I don't have experience with cubieboard but I do have experience with Raspberry PI (home automation, server hosting, video surveillance, motor control). However for this project I believe the two would behave similarly.
Best wishes,
Ionut